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Preliminary Report
Hurricane Ivan
19-27 September 1998

Edward N. Rappaport
National Hurricane Center
18 November 1998

Tropical Storm Alex
Hurricane Bonnie
Tropical Storm Charley
Hurricane Danielle
Hurricane Earl
Tropical Storm Frances
Hurricane Georges
Tropical Storm Hermine
Hurricane Ivan
Hurricane Jeanne
Hurricane Karl
Hurricane Lisa
Hurricane Mitch
Hurricane Nicole

[1998 Atlantic Hurricane Season]

a. Synoptic History

Hurricane Ivan was the first in a trio of hurricanes to form and then remain over the eastern Atlantic Ocean during the latter part of September. The wave from which Ivan developed was rather easily identified by its concentrated area of thunderstorms seen on satellite pictures (not shown) over western Africa near the Greenwich Meridian on 14 September. Although deep convection diminished when the wave neared the coast, the residual cloudiness and sounding data up through 700 mb from Dakar, Senegal showed the system's passage into the Atlantic on the 16th.

Strong convection associated with the wave redeveloped to the south of the Cape Verde Islands on the 17th. Position estimates from satellite analysts began that day. The cloudiness became more concentrated near the apex of the wave on the 18th. Late that day, Dvorak T-numbers first reached 2.0 from the NOAA TPC Tropical Analysis and Forecast Branch (TAFB) and 1.5 from the NOAA Synoptic Analysis Branch (SAB). Slow development followed and it is estimated that the system became a tropical depression near 0000 UTC on the 19th, about 175 n mi to the southwest of the Cape Verde Islands (Fig. 1 [25K GIF] and Table 1).

The tropical cyclone was influenced by mid- to upper-level cyclonic flow centered to its northwest, over the central Atlantic. At first, that pattern consisted of a trough elongated southward from 30N. During Ivan's development, however, water vapor imagery showed the trough become a closed circulation that partially enveloped the tropical cyclone. A second trough later affected Ivan as well. These features influenced the details of Ivan's track (see Fig. 1), which was generally northwestward at 10-15 kt from the 20th-25th.

The troughs also created an environment of vertical shear that led to Ivan's rather slow development (Table 1). Ivan became a tropical storm late on the 20th and during the following 48 hours wind speeds increased to around 55 kt as estimated from the appearance of what could have been an eye on satellite pictures for about an hour.

Ivan's hurricane stage occurred rather far to the north. At 1400 UTC on the 23rd, the eye reappeared and was more prominent than earlier, indicating that Ivan was becoming a hurricane as it neared 30N. After again disappearing, the eye became its most distinct with a diameter of about 20 n mi, and Ivan is estimated to have reached its peak intensity of about 80 kt on the morning of the 26th. The hurricane was then located about 300 n mi to the west of the Azores Islands. At that time, the influence of the upper troughs on Ivan was decreasing and the track of the hurricane was increasingly controlled by the westerlies just to the north. Late on the 26th, the eye disappeared. The inner convective structure rapidly deteriorated while Ivan passed eastward over cooler waters to the north of the Azores Islands on the 27th. Ivan was then becoming a weakening extratropical storm, and then gale, which moved northeastward according to analyses issued in the United Kingdom.

b. Meteorological Statistics

The "best track" intensity was obtained from the data presented in Figs. 2 (12K GIF) and 3 (13K GIF). Those figures show Ivan's estimated central pressure and maximum one-minute wind speed, respectively, versus time. Position and intensity estimates were obtained from analyses of satellite pictures by the SAB and TAFB, and by the Air Force Weather Agency (AFGWC in figures). Analyses also included surface observations.

There were no reports of tropical storm force winds on land.

The ships listed below reported sustained tropical storm force winds. The reports of northerly or northwesterly winds of 35-38 kt from the ship DACF near 16N 25W on 19 September do not seem compatible with other ship reports in that vicinity, or with the analysis of the cyclone--centered a few hundred nautical miles to the southwest at that time. In addition, the speeds shown for ship PJOX at 23/1800 UTC and 24/0300 UTC are probably double the actual winds based on analysis of data by the NWS Marine Prediction Center.

Date/time (UTC)Ship IdLat.(N)Lon.(W)Wind (kt)

c. Casualty and Damage Statistics

Ivan is not known to have caused casualties or damages.

d. Forecast and Warning Critique

The average NHC track forecast errors were about 20% larger than the most-recent 10-year averages, but were comparable in magnitude to most of the numerical model guidance (Table 2). The best performance came from the NOGAPS model.

The NHC generally forecast an intensity for Ivan that was too low by about 10 kt at 24 hours and 20 kt at 72 hours.

Watches and warnings were not issued for Ivan, but NHC advisories did indicate the possibility that tropical storm or hurricane force winds could spread over the Azores.

Table 1. Preliminary best track, Hurricane Ivan, 19-27 Sept. 1998.
revised extratropical stage 1/22/99
Position Pressure
Wind Speed
Lat. (°N)Lon. (°W)
19/000013.426.6101025Tropical Dep.
060013.127.5101025" "
120012.928.2101025" "
180013.129.0101025" "
20/000013.429.6100930" "
060014.330.6100930" "
120015.231.5100830" "
180016.032.6100635Tropical Storm
21/000016.833.7100535" "
060017.434.9100335" "
120018.235.6100335" "
180019.036.0100240" "
22/000020.036.1100140" "
060021.336.1100045" "
120022.936.4 99745" "
180024.237.1 99455" "
23/000025.637.7 99650" "
060026.938.4 99745" "
120028.339.2 99055" "
180029.640.2 98765Hurricane
24/000030.540.9 98665" "
060031.341.6 98570" "
120032.342.0 98570" "
180033.442.3 98570" "
25/000034.442.3 98470" "
060035.341.9 98470" "
120036.341.3 98470" "
180037.240.2 98375" "
26/000038.138.7 98075" "
060039.236.3 97580" "
120040.133.1 97775" "
180040.729.7 98275" "
27/000040.725.7 99460Tropical Storm
060040.922.7 99750Extratropical
120041.319.2100045" "
180041.515.5100240" "
26/060039.236.397580Minimum Pressure

Table 2.
Preliminary forecast evaluation of Hurricane Ivan: Heterogeneous sample.
(Errors in nautical miles for tropical storm and hurricane stages with number of forecasts in parenthesis)
Forecast TechniquePeriod (hours)
CLIP79 (24)155 (22)230 (20)285 (18)348 (14)
GFDI87 (17)179 (15)282 (13)315 (11)461 ( 9)
GFDL*84 ( 9)154 ( 8)240 ( 7)278 ( 5)312 ( 5)
NGPS*81 (11)114 (11)151 (10)175 ( 9)229 ( 5)
NGPI58 (22)99 (20)133 (18)159 (16)246 ( 8)
LBAR64 (24)118 (22)182 (20)250 (18)434 (14)
AVNI122(20)252 (18)345 (15)431 (13)589 (10)
BAMD61 (24)125 (22)207 (20)304 (18)544 (14)
BAMM67 (24)130 (22)203 (20)277 (18)441 (14)
BAMS81 (24)162 (22)241 (20)291 (18)391 (14)
A90E70 (24)124 (22)198 (20)294 (18)501 (14)
UKMI63 (23)105 (22)149 (20)189 (18)298 (12)
A9UK63 (11)109 (10)165 ( 9)222 ( 8)328 ( 7)
NHC OFFICIAL53 (24)114 (22)179(20)241(18)305(14)
(1988-1997 10-year average)
47 (1838)88 (1633)127 (1449) 165 (1006)248 (1006)

* Output not available until after forecast issued.

Jack Beven

Last updated May 1, 1999